The present invention relates to an exhaust purification system for a ship.
Ships, such as a tanker or a transport ship, for example, consume a large amount of power for devices such as various auxiliary machines, a cargo handling device, lights, and an air conditioner. Thus, the ships include a diesel generator as a combination of a diesel engine and a generator that is driven by the diesel engine to generate power to be supplied to an electric system of the devices (see Japanese Unexamined Patent Application Publication No. 2006-341742 and the like). The diesel engine is known as one of internal combustion engines with the highest energy efficiency, and involves a small amount of carbon dioxide in exhaust gas per unit output. Furthermore, the diesel engine can be driven with low quality fuel, such as heavy oil for example, and thus is also economically advantageous.
The exhaust gas, discharged from the diesel engine, includes carbon dioxide, as well as a large amount of nitrogen oxide, sulfur oxide, particulate matters, and the like that are mainly attributable to the heavy oil used as the fuel, and are harmful substances in terms of environmental protection. In particular, nitrogen oxide (hereinafter, referred to as NOx) is harmful to human bodies, highly acidic, and is regarded as a cause of acid rain. Thus, for example, machines driving the diesel generator, such as the ship for example, discharge an extremely large amount of NOx, and thus are regarded as imposing a large load on the global environment.
Generally employed post treatments for largely purifying NOx include selective catalytic reduction (hereinafter, referred to as SCR) using urea as a reductant. Generally, a NOx catalyst having a honeycomb structure is used in SCR. The NOx catalyst is formed of a material in which a support such as an oxide of Ti and the like supports active ingredients such as V and Cr. The aqueous urea solution in a mist form, as a reductant solution, is sprayed to an upstream side of the NOx catalyst. Thus, the aqueous urea solution is hydrolyzed by heat of the exhaust gas, whereby ammonia is produced. This ammonia, serving as the reductant, acts on NOx, whereby NOx is converted into harmless nitrogen and water.